1. Field of the Invention
The present invention relates to baseband receivers, and more particularly to baseband receivers having high sensitivities within a narrow range gate.
2. Description of the Prior Art
A need exists for a sensitive baseband receiver operable within a range gate of several nanoseconds that provides range resolutions in the order of feet. Such a receiver may act as a spatial filter to substantially reduce chaff interference, may be utilized for target profile discrimination, and may act as the clutter filter by adjusting a range gate to provide a range window that excludes the clutter source. A receiver of this type should be held in the "OFF" state except for a short interval, measured in nanoseconds, during which it is switched to the "ON" state. The sensitivity of the receiver in the "ON" state should be in the order of millivolts, while in the "OFF" state it should not respond to signals in the order of half a volt.
To achieve the desired characteristics, it is necessary to attenuate the gain transients by more than 50 dB in a fraction of a nanosecond to prevent false triggering (i.e., receiver triggering on the rise or fall of the range gate pulse itself). Additionally, significant pulse stretching must be performed since the signal can enter the range gate at the beginning or end of the time window, resulting in output pulses that range from a small fraction of a range gate width to a range gate width. These pulses contain insufficient energy to trigger the logic circuit in the following CFAR registers and must be stretched. Baseband receivers of the prior art, such as the types disclosed in U.S. Pat. No. 3,662,316 issued to K. W. Robbins in May 1972 and U.S. Pat. No. 3,750,025 issued to G. F. Ross in July 1973, both assigned to the assignee of the present invention, do not provide the desired sensitivity and in some instances do not possess range gated operation.